Intermediate in the total synthesis of elenolic acid

ABSTRACT

A COMPOUND OF THE FORMULA   2-R4,2-R5,4-(R1-CH(-OH),5-(R-OOC-CH(-R2),6-(R3-OOC-)-   4,5,6,6A-TETRAHYDRO-3AH-CYCLOPENTA-1,3-DIOXOLE   WHEREIN R AND R3 ARE ALKYL OF 1 TO 3 CABON ATOMS, INCLUSIVE, R1 IS ALKYL OF 1 TO 4 CARBON ATOMS R2 IS HYDROGEN OR ALKYL OF 1 TO 4 CARBON ATOMS, AND R4 AND R5 ARE HYDROGEN, ALKYL OF 1 TO 4 CARBON AOMS, INCLUSIVE, OR PHENYL, WITH THE PROVISO THAT ONLY ONE OF R4 AND R5 IS PHENYL, IS PRODUCED IN A MULTISTEP REACTION. THE COMPOUND IS AN INTERMEDIATE FOR ELENOLIC ACID.

-United States Patent t 3, 1 INTERMEDIATE IN THE TOTAL SYNTHESIS V 0F ELENOLIC ACID f 'Robert C. Kelly, Kalamazoo, Mich., assignor to The Upjohn Company, Kalamazoo, Mich.

No Drawing. Original application Aug. 24, 1970, Ser. No.

66,557, now Patent No. 3,703,530, dated'Nov; 21, 1972. Divided and this application-Apr. 12, 1972, Ser.

No. 243,491 I Int. Cl..C07d 13/10 U.s. Cl. 260340.5

1 Claim ABSTRACT OF THE DISCLOSURE I A compound of the formula 000R a .i

H OH CROSS REFERENCE TORELATED APPLICATION This application is a divisional application of application Ser. No. 66,557, filed Aug. 24, 1970, now Pat. No. 3,703,530, issued Nov. 21, 1972.

BACKGROUND OF THE INVENTION (1) Field of the invention The present invention is concerned with a process for the synthesis of elenolic acid, analogs and derivatives thereof and with the intermediates in said process.

(2) Description of the prior art Already in 1931 A. D. Burnett and M. Oliviero [Bull.

Acc. Med. 122, 191 1931)] recognized that an extract from the leaves of the olive tree (Olea furopaea) contained a hypotensive principle [see also L. Panizzi et al., Gazz. Chim. Ital. 90, 1449 (1960)].

W. L. Constantijn Veer, US. Pat. 3,033,877, issued May 8, 1962, described the preparation of elenolic acid, salts, ether-esters and other analogs of elenolic acid. The only method for the preparation of this acid, salts or derivatives thereof was by extraction and chemical treatment of the extnactives of the leaves or the fruit of Olea europaea. In particular the aqueous press juice resulting from pressing the ripe fruit was used. The amount of acid obtained was always exceedingly small; e.g., US. Pat. 3,033,877 reports that from 250 kg. of leaves of Olea europaea 1 14 g. of an impure oil was obtained concerning which it was stated consists for the greater part of "elenolic acid. The same patent reports that from 160 liters of press juice 0.35 g. of elenolide (lactone form of elenolic acid) was obtained. j

The Upjohn Company from a batch of 37,000 liters of olive press juice (obtained in Spain) isolated 1,300 g. of

highly purified calcium elenolate, n'iuch pprer than the material reported above; In additiongj. on'the basisgfi. 1111 clear magnetic resonance, ultraviolet andinfifared data, it was n catedgthat the older. structures are not correct, and that the most likely structure of elenolic acid is:

om-ooorr z The present total synthesis of elenoligacid-and analogs therefore'a significaii'tadva'nce over the preparation from the'r'iatural olive tr'e. a SUMMARY OF THE mvnmii:

The novel process of this inyen'tion and the novel intermediates therein can be illu'stratively represented by the following sequence of :formulae:

.. iii

OOOR materials obtainable the European nd R are alkyl-oil to carbon atoms, inclusiye, wherein R is alkyl of 1;to ,4 carbon atoms, in-

clusiv,:,;whei einR is selected from the group; consisting of hydrogen and alkyl of 1 to 4 carbon atoms, inclusive, wherein R and R are selected from the group consisting of hydrogen, alkyl of 1 to 4 carbon atoms, inclusive, and phenyl, with the proviso that only one of R and R is phenyl, where'i'rfi Xf is selected from the group; consisting movedj a's HX HIoL form a temporary" double bond, and

gwhereinx is selected fromthegroup consisting of those radigal s represented by X and hydroxy. I

The process of this invention comprises: reacting cyclopentadienyl lithium, sodium, or potassium (I) with an alkylating agent of the formula R2 xr-on-ooon (A) wherein R, R fand X are as given above, to give the corresponding 1,3 cycIO entadiene-S-acetic acid alkyl ester (II); reacting II at low temperatures with an alkylmaleiganhydr ide (B) to obtain the corresponding 2,3-dicarboxy 5 norbornene-7-acetic acid alkyl e'ster 2,3-anhydride (III); hydrolyzing III to obtain the corresponding 2,3-dicarboxy-5-norbornene-7-acetic acid alkyl ester (IV);

treating IV with osmium tetroxide, or with a chlorate salt and a catalytic amount. of osmium tetroxicle, to obtain the A dilute aqueous acid hydroxy.

a corresponding 2,3 dicarboxy 5,6-dihydroxynorbornanel-acetic acid alkyl ester (V); treating V with an aldehyde or ketone, preferably acetone, to obtain the corresponding 2,3 dicanboxy 5,6 dihydroxynorbornane-7-acetic acid, alkyl ester, acetal or ketal (VI); subjecting VI to electrolysis in a water-pyridine solution containing 1 to 5% of a tertiary amine such as triethylamine to obtain the corresponding 5,6 dihydroxy 2 norbornene 7 acetic acid, alkyl ester, acetal or ketal (VII); oxidizing VII with aqueous potassium permanganate and sodium periodate to give the corresponding 2-alkanoyl-3,4-dihydroxy-5-carboxycyclopentaneacetic acid, alkyl ester, acetal or ketal (VIII); esterifying (VIII) with an alkanol in the presence of a dehydrating agentsuch as a carbodiimide or with diazoalkane to obtain the corresponding 2-alkanoyl-3,4- dihydroxy 5 carboxycyclopentaneacetic acid, 1,5-dialkyl ester, acetal or ketal (IX) (the two alkyl groups 1 and 5 can be alike or difierent); reducing IX with an alkali metal borohydride to give the corresponding 2-(1-hydroxywith a dilute aqueous acid to give 2-(1-hydroxyalkyl)-3,4-

dihydroxy S-carboxycyclopentaneacetic acid, 1,5-dialkyl ester, 2-ester, e.g., Z-methanesulfonate (XII); oxidizing the glycol XII with aqueous periodate salt to give the corresponding 2 hydroxy 3 (1-hydroxyalkyl)-5-car- I boxy 3,4 dihydro 2H pyran-4-acetic acid, 4,5-dialkyl ester, 3-ester (XIII); heating Compound XIII in a basic medium, pH 7.5 to 9, to give the corresponding Compound XIV, e.g., methyl elenolate when R, R and R are methyl and R is hydrogen. Compound XIV can be selectively hydrolyzed with dilute mineral acid to an acid of Formula XV. If in Formula XV R and R are methyl and R is hydrogen, the acid is elenolic acid.

Alternatively, Compound X can be hydrolyzed with to give Compound XII where X is DESCRIPTION OF THE PREFERRED EMBODIMENTS The alkyl groups herein used having from 1 to 4 carbon atoms, inclusive, such as R and R are illustratively methyl, ethyl, propyl, butyl, isobutyl, secondary butyl and the like. r r

The alkyl groups herein used having from 1 to 8 carbon atoms, inclusive, comprise the group of alkyl groups above with up to 4 carbon atoms, and pentyl, hexyl, heptyl, and octyl and the branched isomers thereof.

The parameter X herein used is a negative element or group which is reactive in metathetic reactions with compounds containing a strong positive element such as sodi- 1.4m,'-. potassium or lithium. Such negative elements or groups are illustratively iodine, bromine, methanesulfonyloxy, butanesulfonyloxy, benzenesulfonyloxy, p-toluenesulfonyloxy and the like.

The parameter X is a negative element or negative group which includes all groups and elements disclosed for X and also chlorine, and OCOR in which R is selected from the group consisting of alkyl of 1 to 8 carbonatoms, inclusive, as illustrated above, and phenyl and Elenolic acid being of low stability is generally used only in the form of salts, such as the calcium salt, sodium salt or as an ester, e.g.,-as methyl or ethyl elenolate. Such products were known to be hypotensive and were U known to be useful in humans and animals as hypotensive agents (see US. Pat. 3,033,877). More recently it was discovered that calcium elenolate and other metal elenolates and esters of elenolic acid are highly virucidal against Coxsackie A-Zl virus, polioviruses l, 2, and 3, rhinovirus strain 209, parainfluenza-3 virus, herpes viruses, vaccinia virus, adenoviruses 1, 2, 3, and 7, respiratory syncitial virus, Newcastle disease virus and others. Saline solution of 1 mg. per ml. of calcium elenolate reduced the viral activity (measured by the number of plaques of viruses present in the sample) as follows:

Likewise, the compound of Formula XIII, XIV, and XV and salts thereof are virucidal and are thus useful to cleanse glassware, apparatus, and hospital equipment from virus contamination when used in solutions of 0.1 to 5 parts per 1000 (weight) in the cleaning solution.

In carrying out the process of this invention a cyclopentadiene alkali metal salt, e.g., cyclopentadienyl lithium, sodium, or potassium (I) is reacted with a negatively substituted alkyl acetate (A) as defined above, e.g., methyl bromo-, iodo-, or methanesulfonyloxyacetate, ethyl 2- bromopropionate, and the like. The reaction is preferably carried out by adding to the cyclopentadiene alkali metal salt, in purified tetrahydrofuran, the substituted alkyl acetate, dropwise, in a nitrogen atmosphere, at a temperature of 10 to 30 C. However, temperatures between and 50 C. are operative. Instead of tetrahydrofuran, diethyl, dipropyl, dibutyl ether, or mixed ethers can be used. An average of 70 to 80% yield of 1,3-cyclopentadiene-S-acetic acid alkyl ester (II) is obtained, which is used in crude form in the next step.

Compound II in its crude form in tetrahydrofuran or an ether as stated above is reacted with an approximately equimolar amount of alkylmaleic hydride at a low temperature, between and 30 C. The reaction period is between 12 hours and 21 days. The thus-obtained product is isolated by conventional procedure, e.g., evaporating the solvent, extraction, crystallization and combinations thereof and is purified by standard methods such as crystallization, chromatography and the like to provide the corresponding 2,3-dicarboxy-5-norbornene-7-acetic acid alkyl ester 2,3-anhydride (HI).

Compound III is hydrolyzed in conventional manner, such as by heating the compound in aqueous 5% sodium or potassium bicarbonate solution between to 60 minutes on the steam bath, and thereafter acidifying the resulting solution to a pH of 3. The product, a 2,3-dicarboxy-5-norbornene-7-acetic acid alkyl ester (IV) precipitates in the aqueous solution and can be easily collected on a filter. Purification of the product is best achieved by crystallizing the precipitated product.

Compound IV is treated with an alkali metal or alkaline earth chlorate salt (e.g., sodium, potassium, calcium, or barium chlorate) and a catalytic quantity of osmium tetroxide. The reaction can be run in partial suspension through the use of water as reaction medium or in solution through the use of mixed solvents such as water-tert. butyl alcohol or water-tetrahydrofuran, and the like. In the preferred embodiment of this invention Compound IV is treated in a water suspension with a 0.1 to 0.5 molar excess of chlorate salt and 0.2 to 1% by weight of osmium tetroxide. The temperature for the reaction is preferably 4050 C., but temperatures between 10 and 75 C. are operative. The reaction time is between 2 and 100 hours and is in general between 5 and 20 hours.

Compound IV can also be oxidized with osmium tetroxide alone, as illustrated in Example 8. The product of the foregoing oxidation, a 2,3-dicarboxy-5,6-dihydroxynorbornane-7-acetic acid alkyl ester (V) is generally isolated -by extraction and the product purified by crystallization.

Compound V is treated with a large excess of an aldehyde or ketone, e.g., acetaldehyde, benzaldehyde, acetone, diethyl ketone, ethyl methyl ketone, dipropyl ketone, acetophenone, or the like in the presence of an anhydrous acid, e.g., hydrogen chloride or hydrogen bromide. In the preferred embodiment of this invention, Compound V is treated with a large excess of acetone which acts as reagent and slurrying agent, in the presence of 5 to 15% of 2,2-dimethoxypropane and 0.1 to 1% of anhydrous hydrogen chloride. The reaction can be carried out at temperatures between 10 to 40 C. during a period of 15 to 120 minutes. The product, a 2,S-dicarboxy-5,6-dihydroxynorbornane-7-acetic acid alkyl ester, acetal or ketal (V1) is iso lated and purified by conventional procedures, e.g., extraction, crystallization, chromatography and the like.

Compound V1 is electrolyzed in a basic medium, e.g., in pyridine-water mixtures with 1-5% (by volume) of trialkylamine present, e.g., triethylamine or tributylamine, or heterocyclic tertiary amines such as l-methylpiperidine, 4-methylmorpholine, and l,4-diaza[2.2.2] bicyclooctane. The electrodes are preferably platinum and the voltage is held between 50 and 100 volts. The reaction mixture is kept to 20 C. or less during the electrolysis. The electrolysis is advantageously carried out by starting the electrolysis with approximately 20% of the solution to be electrolyzed and then adding the remaining portion slowly so as to maintain the amperage at approximately 4 for a voltage of and a termperature of 20 C. The total reaction time is between 4 to 6 hours. The thusproduced 5,6-dihydroxy-2-norbornene-7-acetic acid, alkyl ester, acetal or ketal (VII) is isolated and purified preferably by chromatography, recrystallization, extraction, and the like.

Compound VII is oxidized within a pH range 6.0 to 8.5, with an aqueous solution of permanganate and periodate salts, preferably sodium or potassium permanganate and sodium or potassium periodate, with sodium or potassium bicarbonate present. The oxidizing reagents are used in excess of the required stoichiometric amounts in aqueous concentration of 0.5 to 10% (weight) of oxidant to water. The reaction is carried out at temperatures between 10 and 50 C. during a period of 1 to 8 hours, preferably with stirring. To avoid losses by additional undesired oxidation reactions, the reaction when near completion is terminated by adding sodium sulfite until the permanganate color disappears. The product is preferably isolated by extraction with an organic waterimmiscible solvent, e.g., chloroform, methylene chloride, benzene or the like. The thus-obtained 2-alkanoyl-3,4-dihydroxy-S-carboxycyclopentaneacetic acid, alkyl ester, acetal or ketal (VIII) can be purified by recrystallization.

The acid Compound VIII is esterified by conventional procedures, e.g., with an alkanol and a dehydrating agent such as a carbodiimide, e.g., dicyclohexylcarbodiimide, a sulfonyl chloride, e.g., p-toluenesulfonyl chloride, a chloroformate, e.g., isobutyl chloroformate, and the like, or with a diazoalkane in ether to give a dialkyl ester, 2- alkanoyl-3,4-dihydroxy 5 carboxycyclopentaneacetic acid, 1,5-dialkyl ester, acetal or ketal (1X).

Compound IX is then selectively reduced with a metal hydride, preferably a metal borohydride such as lithium, sodium, or potassium borohydride. In the preferred embodiment of this invention, the borohydride is added in portions over a short period. 10-30 minutes, to a solution of the diester IX in solution. Methanol, ethanol or ether are the preferred solvents for Compound IX. The thusobtained Compound X, a 2-(l-hydroxyalkyl)-3,4-dihydroxy 5 carboxycyclopentaneacetic acid 1,5 -dialkyl ester, acetal or ketal, is isolated and purified by conventional procedures, e.g., extraction, chromatography, crystallization, and the like.

The hydroxy goup of Compound X is then esterified, preferably with methanesulfonyl chloride in pyridine solution at a low temperature, for example, between +10 and 15 C. Other alkane-, alkylbenzeneand benzenesulfonyl halides can be used, as well as alkanoyl, benzoyl,

and p-toluoyl halides and anhydrides, or brominating and chlorinating agents, e.g., N-bromosuccinimide, N-bromoacetamide, thionyl chloride and the like. Extraction and recrystallization provide the corresponding 2-(1-hydroxyalkyl)-3,4dihydroxy carboxycyclopentaneacetic acid, 1,5-dialkyl ester, Z-methanesulfonate, acetal or ketal (X1) or other Formula XI 2-ester.

Compound XI is converted to the corresponding 2-(1- hydroxyalkyl)-3,4 dihydroxy 5 carboxycyclopentaneacetic acid, 1,5-dialkyl ester, 2-ester, e.g., Z-methanesulfonate (XII) by treating it for 1 to 4 hours in aqueous formic acid or in aqueous sulfuric acid, hydrochloric acid or other dilute mineral acids, at a temperature between and 50 C., preferably at room temperature between 22 and 26 C. The product XII is recovered by evaporating the reaction mixture, freeze-drying or chromatography.

Compound XI-I is then treated with excess aqueous alkali metal periodate salt, e.g., sodium or potassium periodate at a pH between 5 and 7 and at a temperature between and 40 C. for 1 to 8 hours, usually from 2 to 4 hours at room temperature and the reaction mixture is extracted with a water-immiscible solvent. The extract contains in solution the corresponding 2-hydroxy-3-(1- hydroxyalkyD-5-carboxy-3,4-dihydro-2H-pyran 4 acetic acid, 4,5-dialkyl ester, 3-ester, e.g., 3-methanesulfonate (XIII). Compound XIII can be obtained by distillation of the solvent and purified b conventional procedures, e.g., crystallization, chromatography, and the like.

Heating a mildly basic solution (preferably aqueous pyridine) containing Compound XIII at 90-100 C. for a period of 10 to 300 minutes gives a 3-formyl-5-carboxy- 3,4-dihydro-2H-pyran 4 acetic acid 4,5-dialkyl ester (XIV). In the case that R, R and R are methyl and R is hydrogen the product XIV is methyl elenolate. Compound XIV is isolated by conventional procedures such as extraction, differential distribution of the product XIV in a solvent system, e.g., Craig extractor or chromatography.

Heating Compound XIV with dilute mineral acid, e.g., 0.1 M sulfuric acid gives 3-formyl-5-carbalkoxy-3,4-dihydro-2H-pyran-4-acetic acid (XV), which in case R and R are methyl and R is hydrogen is free elenolic acid.

The "following preparation and examples illustrate this invention.

Preparation 1.'Cyclope'ntadienyl sodium Metallic sodium (23 g.; lvmole) was pressed into a fineribbon and suspended in freshly purified tetrahydrofuran. A 100 ml. quantity of cyclopentadiene was added in'one portion and the mixture was stirred under nitrogen for 45 minutes. During that period a vigorous reaction oc-' curred, warming the mixture to reflux. After this time an outside heat source,. w'as applied and the reaction mixture was heated under reflux an additional 2 hours. By this time .all of the sodium had reacted. The cyclopentadienyl sodium is extremely sensitive to air and depending .on'the care with which the reaction was run, at this point it showed variation from near colorless through pink to deep-purple. The color did not seem to appreciably affect the yields.

Inthe same manner given above cyclopentadienyl lithium or. potassium can be made.

Example 1.-Methyl 1,3-cyclopentadiene-S-acetate dissolved in deuterochloroform and an NMR taken. Analyses of various runs of the reaction haveindicated 70-80% of the desired isomer (methyl 1,3-cyclopentadiene-S-acetate) and 30-20% of the l-isomer (methyl 1,3-

cyclopentadienel-acetate) Example 2.Ethyl u-methyl-1,3-cyclopentadiene-S-acetate In the manner given in Example 1, cyclopentadienyl sodium was added to ethyl a-bromopropionate to give ethyl a-methyl-1,3-cyclopentadiene-S-acetate.

In the same manner given in Example 1, other alkyl 1,3-cyclopentadiene-S-acetates and alkyl a-alkyl1,3-cyclopentadiene-S-acetates (II) can be made by reacting an alkyl a-bromoalkanoate (A) with cyclopentadienyl anion. Representative compounds, thus obtained, include:

propyl a-ethyl-l,3-cyclopentadiene-S-acetate, butyl a-propyl-1,3-cyclopentadiene-5-acetate, pentyl oa-butyl-1,3-cyclopentadiene-5 acetate, hexyl a-methyl-1,3-cyclopentadiene-S-acetate, heptyl l,3-cyclopentadiene-5-acetate,

octyl 1,3-cyclopentadiene-S-acetate,

isopropyl a-methyl-1,3-cyclopentadiene-S-acetate, isobutyl a-propyl1,3-cyclopentadiene-S-acetate,

and the like.

Example 3.Methyl 2,3-dicarhoxy-2-methyl- 5-norbornene-7-acetate 2,3-anhydride The total crude reaction mixture containing methyl 1,3-cyclopentadiene-S acetate (Example 1) from a 1.5- mole run was treated with 500 g. (4.4 moles) of citraconic anhydride. After distillation of excess solvent at less than 10 C. and lessthan -1" mm., the reaction mixture was allowed to stand 14 days at -13 C. The reaction mixture was then partitioned between methylene chloride and water. The methylene chloride solution was thoroughly washed successively with 5% aqueous sodium bicarbonate solution, water, and saturated brineJThe methylene chloride solution was then dried over anhydrous sodium sulfate and distilled in vacuo, leaving a viscous brown residue. Crystallization of the residue from ether gave 147.5 g. of methyl 2,3-dicarboxy-2-methyl-5-norbornene-7-acetate 2,3-anhydride of melting point -103" C. There was obtained from the mother liquors a second crop amounting to 24.3 g.; melting point 90-105 C.

A sample was prepared for analysis by one more crystallization from'methylene chloride-ether; melting point -108 C. v

Analysis.-Calcd. for C l-1 0 (percent): C, 62.39; H, 5.64. Found (percent): C, 62.28; H, 5.97. I

NMR spectrum (CDCl 6): 1.66 (3H, s.), 2.41 (2H, A B), 2.6 1H, A B), 3.0 (1H, m.),- 3.2 (1H, d., J=4 cps.), 3.6 (1H, m.), 3.65 (3H, s.), 6.30 (2H, AAIQC).

Example 4.Ethyl 2,3-dicarboxy-2-methyl- 5-norbornene-7-acetate 2,3-anhydride In the manner given in Example 3, ethyl 1,3-cyclopentadiene-S-acetate was reacted with citraconic anhydride to give ethyl 2,3-dicarboxy-2-methyl-5-norbornene-7-ace tate 2,3-anhydride. n

In the manner given in Examples 3 and 4, other alkyl 2,3-dicarboxy-2-alkyl and alkyl a-alkyl-LS-dicarbOXy-Z- alkyl 5-norbornene-7-acetate 2,3-anhydrides can be produced by reacting a selected alkyl 1,3-cyclopentadiene-5- acetate or alkyl a-alkyl-1,3-cyclopentadiene-S-acetatewith ethyl a-methyI-Z,3dicarboxy-Z-methyl-5-norbornene-7- acetate 2,3-anhydride, V

propyl methyl-2,3dicarboxy-Zpropyl-5-norbornene-7- acetate 2,3-anhydride,

butyl u-propyl-2,3dicarboxy-2-butyl-5 norbornene-7- acetate 2,3-anhydride,

isopropyl u-butyl-2,3dicarboxy-Z-isobutyl-S-norbornene-7- acetate 2,3-anhydride,

isobutyl a-isobutyl-Z,3dicarboxy-Z-isopropyl-S- r norbornene-7-acetate 2,3-anhydride,

hexyl a-propyl-2,3dicarboxy-2-methyl-5-norbornene-7- acetate 2,3-anhydride,

heptyl a-isopropyl 2,3-dicarboxy-2-methy1-5- norbornene-7-acetate 2,3-anhydride,

octyl ot-methyl-2,3-dicarboxy-Z-methyl-S-norbornene-7- acetate 2,3anhydride,

pentyl 2,3-dicarboxy-Z-ethyl-5-norbornene-7-acetate 2,3-

anhydride,

isopentyl 2,3-dicarboxy-2-methyl-5-norbornene-7- acetate 2,3-anhydride,

methyl a-methyl-2,3-dicarboxy-2-methyl-5-norbornene-7- acetate 2,3-anhydride,

ethyl methyl-2,3dicarboxy-2-butyl-5-norbornene-7- acetate 2,3-anhydride,

and the like.

Example 5.Methyl 2,3-dicarboxy-2-methyl-5- norbornene-7-acetate A 225 g. quantity of methyl 2,3-dicarboxy-2-methyl-5- norbornene-7-acetate 2,3-anhydride was added to 2 l. of water. After stirring for 1 hour at reflux, the reaction mixture was filtered while still hot. On standing and cooling, 192 g. of crystals were deposited; melting point 146- 148 C. A second crop of 14 g. was obtained; melting point 138-l4l C.

A sample was prepared for analysis by one more crystallization from water; melting point 151-152 C.

Analysis.-Calcd. for C H O (percent): C, 58.20; H, 6.01. Found (percent): C, 58.16; H, 6.10. 7

Example 6.Ethyl 2,3-dicarboxy-2-methyl-5- norbornene-7-acetate In the manner give in Example 5, ethyl 2,3-dicarboxy 2-methyl-5 norbornene-7 acetate 2,3-anhydride was hydrolyzed in water to give ethyl 2,3-dicarboxy-2-me-thyl-5- norbornene-7-acetate.

In the manner given in Example 5, other alkyl 2,3-dicarboxy-S-norbornene-7-acetate 2,3-anhydrides of Formula III, as listed above, can be hydrolyzed in water to give the corresponding alkyl 2,3-dicarboxy norbornene 7- acetates. Products thus obtained, include:

1 0 ethyl Zz-ethyl-2,3dicarboxy-2-butyl-5-no1'bornene-7- acetate,

and the like.

Example 7.-Methyl 2,3-dicarboxy-2rmethyl-5- norbornene-7-acetate In the manner given in Example 4, 1 mole of methyl 1,3- cyclopentadiene-S-acetate was reacted with340 g. of citraconic anhydride in tetrahydrofuran.

The tetrahydrofuran was removed by distillation in vacuo at -10 C. The reaction mixture was allowed to stand for 3 days at -13 C. and 2 days at 2 C. The mixture was then poured into 1 liter of water containing 320 g. of sodium carbonate. The resultant mixture was cautiously heated on a steam bathfor 1 hour. It was then cooled, extracted with methylene chloride and then acidified with concentrated hydrochloric acid. The precipitated product was collected by filtration and washed with water. Crystallization of the product from water gave 38.0 g. of methyl 2,3-dicarboxy-2-methyl-5-norbornene-7-acetate of melting point 150-15 1 C. Second and third crops totaling 16.1 g. were obtained; melting point 139-143 C.

Example 8.-Methyl 2,3-dicarboxy-5,6-dihydroxy- 2-methylnorbornane-7-acetate A 106 g. (0.396 mole)quantity of methyl 2,3-dicarboxy- Z-methyl-5-norbornene-7-acetate was dissolved in 750 ml. of tetrahydrofuran and the resultant solution was treated with g. (0.394 mole) of osmium tetroxide in 750 ml. of tetrahydrofuran. The mixture was allowed to stand for three days at 25 C. The resultant black mixture was cooled in an ice bath, stirred and treated with excess hydrogen' sulfide gas. The mixture was filtered free of solids. The filter cake was washed thoroughly with tetrahydrofuran. The filtrate and the washes were combined and evaporated to dryness. Crystallization of the residue from ethyl acetate gave 63.8 g. of methyl 2,3-dicarboxy-5,6-dihydroxy-2-methylnorbornane-7-acetate as off-white crystals of melting point 121-127 C. There was obtained from the mother liquors a second crop amounting to 7.0 g. of product. Total yield 59%. A sample was prepared for analysis by recrystallization from water; melting point 122126 C.

Analysis.Calcd. for C H O (percent): C, 48.75; H, 6.29. Found (percent): C, 48.79; H, 6.42.

Example 9.Methyl 2,3-dicarboxy-5,6-dihydroxy- 2-methylnorbornane-7-acetate A 5.0 g. (19 millimoles) quantity of methyl 2,3-dicarboxy-2methyl-5-norbornene-7-acetate was added to a solution of 3.0 g. (24.5 millimoles) of potassium chlorate and 50 mg. of osmium tetroxide in 125 ml. of Water. The mixture was warmed to 5 0 C. and stirred for 5 hours. The reaction mixture was then cooled and extracted with benzene. The aqueous layer was saturated with sodium chloride and extracted 3 times with tetrahydrofunan. The tetrahydrofuran solution was dried over anhydrous magnesium sulfateand distilled in vacuo, leaving an oil. Crystallization of the oil from ethyl acetate gave 1.95 g. of methyl 2,3 dicarboxy-5,6-dihydroxy-2-methylnorbornane-7-acetate; melting point 129-130 C.

Example 10.-'Ethyl 2,3-dicarboxy-5,6-dihydroxy-2- ethylnorbornane-7-acetate ethyl 2,3-dicarboxy-5,6-dihydroxy-Z-methylnorbornane- 7-acetate,

propyl 2,3 dicarboxy-S,6-dihydroxy-Z-propylnorbornane- 7-acetate,

butyl 2,3-dicarboxy-5,6-dihydroxy-2-butylnorbornane-7- acetate, v i.

isopropyl a-butyl-2,3-dicarboxy-S,6-dihydroxy-2- isobhtylnorbornane-7-acetate,

isobutyl 2,3 dicarboxy-S,6-dihydroxy-2-isopropylnorbornane-7-acet'ate,

hexyl apropyl-2,3-dicarboxy-5,6-dihydroxy-2- methylnorbornane-7-acetate,

heptyl 2,3-dic=arboxy-5,6-dihydrovy-2-ethy1- norbornane-7-acetate, octyl a-methyl-2,3-

dicarboxy-5,6-dihydroxy-2-propylnorbornane-7-acetate,

pentyl 2,3-dicarboxy-5,6 dihydroxy-2-ethylnorbornane-7-acetate, isopentyl 2,3-dicarboxy-5,6- dihydroxy-Z-methylnorbornane-7-acetate,

methyl a-methyl-Z,3-dicarboxy-5,6-dihydroxy-2- methylnorbornane-acetate,

ethyl a-ethyl-2,3-dicarboxy-5,6-dihydroxy-2- butylnorbornane-7-acetate,

and the like.

Example 11.Methyl 2,3-dicarboxy-5,6-dihydroxy-2- methylnorbornane-7-acetate acetonide A 128 g. (0.424 mole) quantity of methyl 2,3-dicarboxy 5,6 dihydroxy-2-methylnorbornane-7-acetate was slurried in 2 l. of acetone and 160 ml. of 2,2-dimethoxypropane. The slurry was treated with 4 ml. of 2.4 M hydrogen chloride in anhydrous dioxane, causing the suspended solid to dissolve immediately. After /2 hour, the solution was evaporated to dryness in vacuo leaving, when completely dry, 140 g. of crystals of methyl 2,3-dicarboxy- 5,6 dihydroxy Z-methylnorbornane-7-acetate, acetonide suitable for further use. A sample was prepared for analysis by one recrystallization from benzene-acetone; melting point 154155 C.

Analysis.-Calcd. for C H O (percent): C, 56.15; H, 6.48. Found (percent): C, 56.25; H, 6.57.

Example 12.-Methyl a-methyI-Z,3-dicarboxy-5,6-dihydroXy-2-methylnorbornane-7-acetate acetonide In the manner given in Example 11, methyl u-methyl- 2,3 dicarboxy-S,6-dihydroxy-2-methyl-norbornane-7-acetate was treated with 2,2-dimethoxypropane in acetone to give methyl a-methyl-2,3-dicarboxy-5,6-dihydroxy-2-methylnorbornane-7-acetate acetonide.

In the manner given in Example 11, other alkyl 2,3-dicar-boxy 5,6 dihydroxy-2-alkylnorbornane-7-acetic acid ketals or acetals can be prepared by reacting an alkyl 2,3- dicarboxy-S,6-dihydroxy-2-al'kylnorbornane-7-acetate with a ketone or aldehyde. Representative compounds, thus' obtained, include:

The acetonide, methyl ethyl ketal, diethyl ketal, propyl ethyl ketal, formaldehyde acetal, 'acetaldehyde acetal, and propionaldehyde acetal and the like of ethyl 2,3-dicarboxy-5,6-dihydroxy-2-methylnorbornane-7- acetate, 1

propyl 2,3-dicarboxy-5,6-dihydroxy-Z-propylnorbornane-. 7-acetate, I l

butyl m-propyl-2,3-dicarboxy-S,6-dihydroxy-2-butylnorbornane-7-acetate,

isopropyl a-butyl-2,3-dicarboxy-5,6-dihydroxy-2-isobutylnorbornane-7-acetate,

isobutyl 2,3-dicarboxy-5,6-dihydroxy-Z-isopropylnorbornane-7-acetate,

hexyl a-propyl-2,3-dicarboxy-5,6-dihydroxy-2-methylnor bornane-7-acetate,

heptyl 2,3-dicarboxy-S,6-dihydroxy-2-ethylnorbornane-7- acetate,

octyl a-methyI-Z,3-dicarboxy-5,6-dihydroxy-2-propylnorbornane-7-acetate,

pentyl 2,3-dicarboxy-5,6-dihydroxy-2-ethylnorbornane-7- acetate,

12 isopentyl 2,3-dicarboxy-5,6-dihydroxy-Z-methylnorbon nane-7-acetate, methyl u-methyl-Z,3-dicarboxy-5,6-dihydroxy-2-methylnorbornane-7-acetate, ethyl a-ethyl-2,3-dicarboxy-5,6-dihydroxy-2-butylnorbornane-7-acetate,

and the like.

Example 13.--Methyl 2-methyl-5,6-dihydroxy-2-norbornene-7-acetate acetonide (VII when R, R R and R are methyl; R is hydrogen.)

A 5.1 g. (15 millimoles) quantity of methyl 2,3-dicarboxy 5,6 dihydroxy-Z-methylnorhornane-7-acetate ace tonide was dissolved in 200 ml. of'pyridine: water (90:10 by volume) and 3.75 ml. of triethylamine. The resultant solution was electrolyzed using platinum wire mesh electrodes held between 60 and 90 volts. The reaction temperature was maintained throughout at 15-20 C. using a solid carbon dioxide-acetone bath. The initial value for the amperage under these conditions was 4. The amperage was maintained at this value by the gradual addition of a solution of 20.5 g. of methyl 2,3-dicarboxy-5,6-dihydroxy-2-methylnorbornane-7-acetate acetonide in 100 m1. of pyridinezwater (90:10 by volume) and 3.75 ml. of triethylamine. The addition was completed in about 1.5

hours, after which the reaction was allowed to proceedtill the amperage fell below a value of one (about 5 hours total reaction time). The mixture was evaporated to dryness in vacuo and the residue was partitioned between 1 N hydrochloric acid and methylene chloride. The methylene chloride layer was washed successively with 1 N hydrochloric acid, 5% aqueous sodium bicarbonate and saturated brine, and dried over anhydrous sodium sulfate. Distillation of the methylene chloride left a dark brown residue which was combined with the crude residues from two similar runs. Chromatography on 2 kg. of silica gel, eluting with methanolzmethylene chloride (3:97 by volume) gave two compounds. The faster moving was easily detectable on thin layer chromatography wth KMnO NalO reagent and was found by NMR to be the desired methyl 2 methyl 5,6-dihydroxy-2-norbornene-7-acetate acetonide.

The yields of this compound varied from 25% on the scale described above to greater than 50% on l-gram runs.

IR spectrum (mineral oil mull): 1735, 1625, 1265, 1200, 1180, 1050, 1030, 855.

Example l4.- -Methyl a,2-dimethyl-5,6-dihydroxy-2-norbornene-7-acetate acetonide 1 In the manner given in Example 13, methyl a,2-dimeth 'yl 2,3-dicarboxy-5,6-dihydroxynorbornane-7-acetate acetonide was decarboxylated in pyridine-Water in the presence of triethylamine, with an electric current, to give methyl ,2 dimethyl-S,6-dihydroxy-2-norbornene-7-acetate acetonide.

In the manner given in Example 13, other alkyl 2,3- dicarboxy 5,6 dihydroxynorbornane-7-acetate ketals or acetals can be converted to the corresponding alkyl 2- alkyl 5,6 dihydroxy-Z-norbornene-7-acetate ketals or acetals by means of electric current.

- Representative compounds, thus obtained, include:

V and thelike.;,

Example "l5.'-"-Meth'yl 2 acetyl-3,4-dihydroxycarboxycyclopentane-acetate acetonide (VII, wherein R, R R and R are methyl; R is hydrogen) 1 A quantity 059.6 g. (38 millimoles) of methyl 2-methyl 5,G-dihydroxy-2-norb0rnene-7-acetate,acetonide was treated with 9.6 g. of solid sodium bicarbonate followed by 960 ml. of an aqueous solution containing 46.4 g. (218 millimoles) of sodium periodate and 0.9 g. (5.7 millimoles) of potassium permanganate. The reaction mixture was stirred vigorously for 4% hours. The mixture was then cooled in an ice-bath and solid sodium sul-fite slowly added until the potassium permanganate color disappeared. This solution was then extracted with methylene chloride. The aqueous layer was acidified to pH 2 and extracted 3 times with methylene chloride. The combined methylene chloride solutions were washed with saturated brine and dried over anhydrous sodium sulfate. Distillation of the methylene chloride in vacuo left 6.9 g. of oil which solidified on standing.- Crystallization of this mate rial from benzene-Skellysolve B hexanes gave 4.1 g. of crystalline methyl 2-acetyl-3,4-dihydroxy-S-carboxycyclopentaneacetate acetonide; melting point 8793 C. A second and third crop were obtained and combined, giving another 1.0 g.; melting point 87-93 .C. A sample was prepared for analysis bygone'further crystallization from benzene-Skellysolve ,B hexanes; melting point 91-93 C. Analysis-Calm. for C I-1 0 (percent): 0, 55.99; H, 6.71. Found (percent): C, 55.71; H, 7 .00.

Example 16;-Methyl a-methyl-2-acetyl-3,4-dihydroxy- S-carboxycylopentaneacetate acetonide,

octyl a-butyl-Z- acetyh3,4 dihydroxy-S-carboxycyclopentaneacetate methyl butyl ketone ketal,

isopentyl u-ethyl-2-acetyl-3,4-dihydroxy-5-carboxycyclopentaneacetateacetonide,

ethyl a-isopropyl-2epropionyl-3,4-dihydroxy 5-carboxy- 'cyclopentane acetate, acetonide,

propyl a ethyl-2-propionyl-3,4-dihydroxy-5-carboxy- I :xecyclopentaneacetate acetonide, 1

ethyl a-butyl-2-valeryl-3A-dihydroxy-5-carboxycyclopentaneacetate acetonide,

andthe like. Example 17-?21acetyl-3,4-dihydroxy-S-carboxycyclo:

,pentaneabeticacid 1,5-dimethyl ester, acetonide A 4.1, g. sample of methyl 2-acetyl-3,4-dihydroxy-5- carboxycyclopentaneacetate acetonide was dissolved in ether and treated with excess ethereal diazomethanel The solution was, then evaporatedto dryness, leaving 4.3 g. oflc'olorless oil, suitable for the next reaction. A small sample was chromatographed on silica gel. The desired material was eluted with methanolzmethylene chloride (2.5 :97.5-by volume). Distillation of the solvent from the center fractions containing the product as indicated by thin layer chromatography left an oil, 2-acetyl-3,4-dihydroxy- 5 carboxycyclopentaneacetic acid 1,5-dimethyl ester, acetonide.

.Analysis.Calcd. for (3 E 0, (percent): C, 57.31; H, 7.06. Found (percent): C, 57.14; H, 7.04.

Example 18.a-methyl-2-acetyl-3,4-dihydroxy-5-carboxycyclopentaneacetic acid 1,5-dimethyl ester, acetonide In the manner given in Example 17, methyl a-methyl- 2-acetyl-3,4-dihydroxy 5 carboxycyclopentaneacetate acetonide was treated with excess diazomethane in diethyl ether to give m-methyl-2-acetyl-3,4 dihydroxy-5-carboxycyclopentaneacetic acid 1,5-dimethyl ester, acetonide.

In the manner given in Example 17, other 2alkanoyl- 3,4-dihydroxy-5-carboxycyclopentaneacetic acid 1,5-dialkyl ester acetals or ketals can be produced by reacting a selected alkyl 2-alkanoyl-3,4-dihydroxy-S-carboxycyclopentaneacetate acetal or ketal with a diazoalkane. Representative compounds, thus obtained, include:

a-ethyl-2-propionyl-3,4-dihydroxyS-carboxycyclopen- In the manner given in Example 15, methyl a,2-dimethyl-5,6-dihydroxy-2-norbornene 7' acetate actonide was converted with sodium bicarbonate, sodium periodate and potassium peimanganate to methyl u-methyl-2-acetyl-3,4- dihydroxy 5-carboxycyclopentaneacetate actonide.

In the same manner given in Example 15, other alkyl 2-alkyl-5,6-dihydfoxy-2-norbornene-7-acetate a'cetals and ketals are converted tothe-correspondingallryl- Z-alkanoyk 3,4-dihydroxy-S-carboxycyclopentaneacetate acetals and ketals.

Representative compounds, thusproduced, include;

ethyl ot-ethyl-2-propionyl-3,4-dihydroxy-5-carboxycyclopentaneacetate acetonide,

propyl a-propyl-2-butyryl-3,4-dihydroxy-5-carboxycyclopentaneacetate acetonide,

butyl a-butyl-2-valeryl-3,4-dihydroxy-5-carboxycyclopentaneacetate acetonide,

isopropyl a-methyl-2-acetyl-3,4-dihydroxy-5-carboxycyclopentaneacetate benzaldehyde acetal,

isobutyl u-ethyl-2-butyryl-3,4-dihydroxy-5-carboxycyclopentaneacetate diethyl ketone ketal,

pentyl a-propyl-2-valeryl-3,4-dihydroxy-5-carboxycyclopentaneactate methyl ethyl ketone ketal,

hexyl a-isopropyl-Z-isobutyryl-3,4-dihydroxy-5-carboxycyclopentaneacetate formaldehyde acetal,

heptyl u-butyl-2-butyryl-3,4-dihydroxy-5-carboxycyclopentaneacetate acetonide,

taneacetic acid 1,5-diethyl ester, acetonide, a-propyl-2-butyryl-3,4-dihydroxy-S-carboxycyclopentaneacetic acid l-ethyl-S-propyl ester, acetonide, a-butyl-2-valeryl-3,4-dihydroxy-S-carboxycyclopentaneactic acid l-methyl-S-ethyl ester, acetonide, a-methyl-2-acetyl-3,4-dihydroxy-S-carboxycyclopentaneacetic acid I-butyl-S-methyl ester, benzaldehyde acetal, 2-acetyl-3,4-dihydroxy-S-carboxycyclopentaneacetic acid l-propyl-S-ethyl ester, diethyl ketone ketal,

u-methyl-2-valeryl-3,4dihydroxy-5-carboxycyclopentaneand the like Example 19. -2- (l-hydroxyethyl)=3,4-dihydroxy-5-carboxycyclopentaneacetic acid 1,5-dimethyl'ester, acetonide p, l

A 3.7 g. (11.8 millimoles) quantity of- 2-acetyl-3,4- dihydroxy-5-carboxycyclopentaneacetic acid 1,5-dimethyl ester, acetonide was dissolved in 20 ml. of methanol and the solution was cooled to C. in aniice-salt bath. Over a period of 15 minutes, 334mg. of sodium borohydride was added. After a total of 60 minutes, 0.53 ml. of acetic acid was added and the solution was evaporated to dryness. The residue was partitioned between methylene chloride and water. The methylene chloride layer was separated and combined with a methylene chloride wash of the water layer. The methylene chloride solution'was'washed with saturated brine and dried over anhydrous sodium sulfate. Distillation of the methylene chloride'in 'vacuo left anessentially quantitative yield of oily residue, which 'was shown by NMR spectroscopy not to contain any detec'table starting material but rather showed the product to consist of a nearly equal mixture of the diastercomeric alcohols, 2-( l-hydroxyethyl)-3,4 dihydroxy--carboxycy clopentaneacetic acid 1,5-dirnethyl ester, acetonide.

Example 20.z-methyl 2 1- hydroxyethyl) -3,4-dihy droxy-5-carboxycyclopentaneacetic acid 1,5 dimethyl ester, acetonide In the manner given in Example, 19, a-methyl-Z-acetyl- 3,4-dihydroxy-S-carboxycyclopentaneacetic acid 1,5-dimethyl ester, acetonide was reduced with sodium borohydride to give a mixture of the two diastereoisomeric alcohols, a-methyl-2-(l-hydroxyethyl) 3,4 dihydroxy-S-carboxycyclopentaneacetic acid 1,5-dimethyl ester, acetonide.

In the same manner given in Example 19, other 2-(1- hydroxy-alkyl)-3,4-dihydroxy-1,5-dialkyl ester, acetals or ketals can be prepared by reducing the corresponding 2- alkanoyl-3,4-dihydroxy-5-carboxycyclopentaneacetic acid 1,5-dialkyl ester, acetals or ketals with an alkali metal borohydride. Representative compounds, thus prepared include:

a-ethyl-2-( 1-hydroxypropy1)-3 4-dihydroxy-5-carboxycyclopentaneacetic acid 1,5-diethyl ester, acetonide, a-propyl-2- l-hydroxybutyl -3 ,4-dihydroxy-5-carb oxycyclopentaneacetic acid 1,5-diethyl ester, acetonide, u-butyl-2-( l-hydroxypentyl) -3,4-dihydroxy-5-carboxy cyclopentaneacetic acid l-ethyl-S-propyl ester, acetonide, a-methyl-Z- l-hydroxyethyl) -3,4-dihydroxy-5 carboxycyclopentaneacetic acid l-methyl-S-ethyl ester, benzaldehyde acetal, 1 2- l-hydroxyethyl -3 ,4-dihydroxy-5-carboxycyclopen- 1tjrneacetic acid l-butyl-S-methyl ester, diethyl ketone etal, a-methyl-2- l-hydroxypentyl) -3,4-dihydroxy-5-carboxycyclopentaneacetic acid l-propyl-S-ethyl ester, methyl ethyl ketone ketal, a-ethyl-2-( l-hydroxyethyl) -3 ,4-dihydroxy-5-carboxycyclopentaneacetic acid l-heptyl-S-propyl ester, formaldehyde acetal,

and the like.

I Tclairn: v V A compound of the formulaz' wherein R and R are alkyl-of lto 8'rcarbon atoms,in-v clusive, wherein R is alkyl of .1=to 4 carbon atoms, in-' clusive, wherein R is selected from the group :consisting of hydrogen and alkyl of 1*t'o4 carbon atoms, inclusive, and wherein R and R are selected from the group consisting of hydrogen, alkyl of 1 to 4 carbon atoms, inclusive, and phenyl, with the proviso that only one of R and R is*phenyl.

I 7' References Cited I V UNITEDSTATES ,BATENTS, 3,033,877 5/1962 Veer .260, -.-34s.8

NICHOLAS SLRIZZQPrimary Examiner 1 I. H. TURNIPSEED, Assistantf'Examineri' methyl UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION PATENTNO.: 5,795,3 6

DATED I Feb rua ry 19, 1974 INVENTOR(S) Robert C. Kel ly It is certified that error appearsin the above-identified patent and that said Letters Patent are hereby corrected as shown below: 0

Col umn 2, l i ne 40-45, Formula I l i should appea r as shown below i nstead of as i n the patent:

Col umn 6, l i ne 71, "goup' should read g roup Col umn 9,

line 46, "give in" should read given in Column 11,

Gr l ine ll, "5,6-dihydrovy" should read 5,6-di hyd roxy Column 15, line 19, "(Vll," should read (Vlll, line 53,

"actonide" should read acetonide line 71, "cyclopentaneactate" should read cyclopentaneacetate Column 14, 'line 48, "actic acid" should read --acetic acid Signed and Scaled this Third Day of August 1976 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN Am'slr'ng Officer (ummrsirr'nner uj'larenrs and Trademarks 

